Which one is more potent?
essential oils or fragrance oils?
Explain what you mean by 'potent', please? Are you talking about usage rates?
Seriously, though, there are hundreds of different plant based essential oils. There are thousands of manufactured fragrance oils, and some of these manufactured FO's do contain essential oils in addition to synthetic aroma chemicals. There is no one-size-fits-all answer.
Some essential oils, especially citrus oils, fade very quickly. Others, like patchouli, can last for years. Most fall somewhere in the middle. Same with fragrance oils.
If you are asking this question in relation to lotion, either essential oils or fragrance oils will be fine. Your preference. Your preservative will stop preserving, or your oils will go rancid before a fragranced product in a closed container will lose it's scent. If you don't preserve, it will probably mold first.
The best thing to do is experiment with scents you like, to see how long they last. Make sure you buy fragrance oils that are skin-safe, if you go that route. Some fragrances are made for candles and may use ingredients not recommended for skin contact. Some essential oils, like cinnamon, may be irritants if used in more than the tiniest amount.